PROJECT SUMMARY Women with oral cancer experience more cancer pain than men. Our preliminary analysis of a cohort of 91 oral cancer patients (47 men, 44 women) accrued through the NYU Oral Cancer Center demonstrated a sex difference in self-reported oral cancer pain as measured by the validated UCSF Oral Cancer Pain Questionnaire. However, the etiology of oral cancer pain is unknown. I recently demonstrated a sex difference in the prevalence and severity of oral squamous cell carcinoma (oSCC)-induced pain using the 4- nitroquinoline-1-oxide (4NQO)-induced oral carcinogenesis mouse model. Female mice with oSCC exhibit significantly more pain behavior compared to male mice. Furthermore, using flow cytometry to quantify inflammation and classify immune cell infiltrate, I revealed significant differences in the immune cell infiltrate in the cancer microenvironment of male and female mice. Tongues from male mice with oSCC had a 4-fold increase in infiltrating neutrophils but female mice did not. I hypothesize that infiltrating neutrophils in the cancer microenvironment contribute to the sex differences in oral cancer pain. In support of my hypothesis, I have shown that opioids are expressed by neutrophils isolated from the tongue cancer-induced inflammatory microenvironment in mice. Furthermore, in the presence of tongue cancer-induced inflammation, local naloxone (opioid receptor antagonist) treatment potentiated pain behavior in male mice only. To further test my hypothesis, I will investigate whether abundance of infiltrating neutrophils correlates with oral cancer pain and sex in human patients (Aim 1) as well as determine if manipulation of neutrophil infiltration modifies pain behavior in 4NQO-treated tumor-bearing male mice (Aim 2). In the proposed experiments, I will employ a translational research strategy focused on the neurobiology of oral cancer pain through which I will gain requisite training in oral histopathology, clinical-translational research, as well as selective manipulation of immune infiltrate in a cancer mouse model. The successful completion of the proposed experiments will further my knowledge in the relationship between cancer, associated inflammation, and pain as well as development of the skills that I need to independently pursue clinical-translational research.